Long-term Survival Outcomes of Synchronous Colon Cancer: A Cross-Sectional Population-Based Comparative Analysis

BACKGROUND: – Synchronous colon cancer is defined as two or more primary colon cancers diagnosed simultaneously or within six months. It comprises 3-5% of all colon cancer diagnoses. Although increased risk of postoperative morbidity has generally been reported, the impact on long-term outcomes remains unclear. OBJECTIVE: – This study primarily evaluated the impact of synchronous colon cancer on disease-free and overall survival as compared to solitary tumors in the total population, and secondarily in stratified subgroups by sidedness and by stage of the most advanced tumor. DESIGN: – This was a retrospective, observational, cross-sectional, collaborative, multicenter, population-based study. The dominant tumor of synchronous cancers was determined by pathological stage and clinical features. Bilateral tumors were defined as synchronous left- and right-sided tumors. SETTINGS: – Multicenter collaborative research involving 50 Dutch hospitals. PATIENTS: – Patients with a curatively intended oncological resection for stage I-III colon cancer, between January 1, 2014, and December 31, 2015, were included. Follow-up details were provided by local collaborators from October 2021 until June 2024. MAIN OUTCOME MEASURES: – Disease-free and overall survival. RESULTS: – A total of 7, 982 patients with stage I-III colon cancer were included, of whom 269 patients (3.4%, 95% CI 3.0-3.8) had synchronous colon tumors. Of those, 155 patients (58%) had a right-dominant tumor and 190 (71%) had unilateral tumors. Median follow-up was 60.1 months (IQR 36.2-68.8). No differences between solitary and synchronous colon cancer were found regarding 5-year disease-free survival (70.0% ± 0.01 vs 65.7% ± 0.03, p = 0.10) and overall survival (75.5% ± 0.01 vs 72.4% ± 0.03, p = 0.59), neither after stratification for stage. No differences in disease-free or overall survival between unilateral and bilateral synchronous colon cancer, nor between right-dominant versus left-dominant synchronous colon cancer were observed. LIMITATIONS: – A limitation of this study was its retrospective nature. CONCLUSIONS: – This study demonstrated no significant differences for 5-year disease-free and overall survival between solitary and synchronous colon cancer, neither between subgroups of synchronous colon cancer depending on tumor location. See Video Abstract.